As is well known, orientatable mountings of the type indicated are used together with stands, tripods or other supports in the context of optical equipment and in particular in the specific sector of photo-cinematographic equipment to support such equipment in an orientatable way.
In known arrangements it is typically provided that one or more universal joints, for example of the spherical or cylindrical type, provided on the mounting for orientatable positioning of the same can be immobilized in the preselected spatial position through the application of friction locking forces exerted by means of pressure screws acting directly on the components of the joints or through the intermediary of resilient spring means.
Other known arrangements provide for the use of means applying a load of the hydrostatic type, for example comprising hydraulic piston devices to which a hydraulic thrust produced by adjusting the pressure within the piston chamber is transferred. One example of a hydrostatic system for immobilizing the universal joint of an orientatable mounting is known from U.S. Pat. No. 4,886,230.
Although advantageous in comparison with systems of a solely mechanical nature, in particular through the greater efficiency which can be obtained in applying the immobilizing forces, the hydrostatic immobilizing system proposed nevertheless has some limitations both in terms of the accuracy of positioning and gradual application of immobilizing forces to the joint which can be achieved, particularly when adjusting the so-called friction load, which is separate from the effective immobilizing load and is created between the components of the joint to permit readier and more accurate positioning movement of the mounting with respect to the support.